Beeping sound with jacks up

If the fluid level in them is only slightly low, they'll beep. I had to add what amounted to a couple of tablespoons to stop mine from beeping. Mine had worked just fine for a couple of years and then they started beeping one morning when I raised them. I checked the fluid level and it looked fine. There was no leakage that I could find so I don't know why they started beeping.

Bill